1. Field of the Invention
The present invention relates to a method of detecting position/speed of a moving body and apparatus therefor.
Here, although the "moving body" is represented by rotary motors, linearly moving actuators, and so on, those matters similar to the rotary motors, the linearly moving actuators, and so on are also included in the concept of the "moving body". In a wide meaning, the matters similar to these include forward and backward moving tables and turntables in machining tools, arms and turning elements of robots, and the like.
2. Description of the Prior Art
As the means for detecting the position and speed of a moving body, we have proposed those disclosed in the specification and drawings of U.S. Pat. No. 4,621,224.
In the means proposed in the U.S. Pat. No. 4,621,224, the position of a moving body is detected on the basis of an output signal of a two-phase encoder which is arranged to detect relative positions of a moving body and another body which is positioned in a stationary state relative to the moving body, that is to say, two bodies which move relative to each other.
Specifically, the values of two-phase periodic or rectangular waves which serve as predetermined carrier waves are compared with a specific value such as a zero voltage, so that pulse signals are generated at the zero-cross points of the waves. The pulse signals are stored in a storage circuit. The finely estimated position between the pulse signals is detected from the analog values of the periodic waves.
According to the U.S. Pat. No. 4,621,224, the detection of a position between the pulse signals is carried out by interpolation control or by prediction control by an observer. Accordingly, it is difficult to detect an absolute position. In short, each pulse for detecting a roughly estimated position is generated at the zero-cross point of the periodic wave, but the position of generation of the pulse varies widely because of the chattering of the pulse when noise is superimposed on the periodic wave as an analog signal. As a measure counter to the trouble, known is a technique in which hysteresis is given to the specific value to form two reference values (thresholds) to thereby prevent operation error caused by noise.
If hysteresis is given to the specific value, however, the position of generation of the pulse for detecting the roughly estimated position does not always agree with the finely estimated position. Consequently, the position, especially the finely estimated position detected, becomes discontinuous.